WO2007033934A2

WO2007033934A2 - Method for determining tortuosity, catalyst support, catalyst, and method for dehydrogenating hydrocarbons

Info

Publication number: WO2007033934A2
Application number: PCT/EP2006/066370
Authority: WO
Inventors: Simon Falk; Sven Crone; Götz-Peter SCHINDLER; Ulrich Müller; Frank Stallmach; Wiete SCHÖNFELDER
Original assignee: Basf Se
Priority date: 2005-09-20
Filing date: 2006-09-14
Publication date: 2007-03-29
Also published as: WO2007033934A3; US20070099299A1

Abstract

The invention relates to a catalyst support and to catalysts comprising said support and having a defined tortuosity. The invention also relates to the use thereof for heterogeneous catalytic hydrogenation processes of hydrocarbons.

Description

Catalyst support, catalyst and process for dehydrogenating hydrocarbons

description

The invention relates to a catalyst carrier, a dehydrogenation catalyst and a process for the heterogeneously catalyzed dehydrogenation of C ₂ -C ₃ o-hydrocarbons, preferably of C ₂ -C ₁ 5, more preferably from C ₂ -C8- and most preferably C ₃ and C ₄ hydrocarbons. Hydrocarbons are preferably understood as meaning chemical compounds which are composed exclusively of C and H. Particularly advantageous is the heterogeneously catalyzed dehydrogenation of saturated hydrocarbons according to the invention. Furthermore, the invention relates to a method for determining the tortuosity of a porous catalyst support.

Dehydrogenated hydrocarbons are required as starting materials for numerous industrial processes in large quantities. For example, dehydrogenated hydrocarbons find use in the manufacture of detergents, anti-knock gasoline and pharmaceutical products. Likewise, many plastics are produced by polymerization of olefins.

For example, acrylonitrile, acrylic acid or C ₄ -oxo alcohols are produced from propylene. Propylene is currently produced predominantly by steam cracking or by catalytic cracking of suitable hydrocarbons or hydrocarbon mixtures such as naphtha.

Propylene can also be prepared by heterogeneously catalyzed dehydrogenation of propane.

In order to achieve acceptable conversions in the case of heterogeneously catalyzed dehydrogenations even with a single reactor pass, it is generally necessary to work at relatively high reaction temperatures. Typical reaction temperatures for heterogeneously catalyzed gas phase dehydrogenations are at 300 to 700 ° C. As a rule, one molecule of hydrogen is produced per molecule of hydrocarbon.

The dehydrogenation of hydrocarbons is endothermic (secondary or simultaneous combustion of the hydrogen formed can provide for heat balance). The dehydrogenation heat needed to establish a desired conversion must either be supplied to the reaction gas in advance and / or in the course of the catalytic dehydrogenation. In most known dehydrogenation processes, the dehydrogenation heat is generated outside the reactor and is added to the reactor. supplied onsgas from the outside. This requires complex reactor and process concepts and leads at high conversions to steep temperature gradients in the reactor, with the risk of increased by-product formation. Thus, for example, a plurality of adiabatic catalyst beds can be arranged in successively connected annular gap reactors. The reaction gas mixture is overheated by heat exchangers on its way from one catalyst bed to the next catalyst bed and then cools again during the subsequent reactor passage. In order to achieve high conversions with such a reactor concept, the number of reactors connected in series or the reactor inlet temperature of the gas mixture must be increased. The resulting overheating inevitably leads to increased by-product formation by cracking reactions. It is also known to arrange the catalyst bed in a tubular reactor and to generate the Dehydrierwärme by the combustion of combustible gases outside the tubular reactor and coupled via the pipe wall into the interior of the reactor. In these reactors, high conversions lead to steep temperature gradients between the wall and the interior of the reaction tube.

An alternative is the generation of the dehydrogenation heat directly in the reaction gas mixture of the dehydrogenation by oxidation of hydrogen formed or additionally supplied during the dehydrogenation or of hydrocarbons present in the reaction gas mixture with oxygen. For this purpose, an oxygen-containing gas and optionally hydrogen is added to the reaction gas mixture either before the first catalyst bed or before subsequent catalyst beds. The heat of reaction liberated during the oxidation prevents large temperature gradients in the reactor even at high conversions. At the same time a very simple process concept is realized by dispensing with indirect reactor heating.

Catalysts for heterogeneously catalyzed dehydrogenations are normally solid bodies which consist of an inert main body (support) and of an active mass applied to it (in particular to its inner surface). One speaks also of supported catalysts. The carrier usually differs from the active material in that it is unable to catalyze the dehydration. That is, the dehydrogenation conversions (in .mu.m% of the starting compound) achieved in its presence or in its absence under otherwise identical dehydrogenation conditions are usually less than 5 .mu.m%, preferably less than 3 mol%, and particularly preferably less than 1 mol% of each other.

US Pat. No. 4,788,371 describes a process for the water vapor dehydrogenation of dehydrogenatable hydrocarbons in the gas phase in conjunction with an oxidative reheating of the intermediate products, wherein the same catalyst is used for the selective oxidation. dation of hydrogen and the Wasserdampfdehydrierung is used. In this case, hydrogen can be supplied as a co-feed. The catalyst used contains a Group VIII noble metal, an alkali metal, and another Group B, Ga, In, Ge, Sn, and Pb metal on an inorganic oxide support such as alumina. The process can be carried out in one or more stages in a fixed or moving bed.

WO 94/29021 describes a catalyst comprising a support consisting essentially of a mixed oxide of magnesium and aluminum Mg (Al) O and a Group VIII noble metal, preferably platinum, a Group IVA metal, preferably tin, and optionally one Alkali metal, preferably cesium. The catalyst is used in the dehydrogenation of hydrocarbons, which can be carried out in the presence of oxygen.

US 5,733,518 describes a process for the selective oxidation of hydrogen with oxygen in the presence of hydrocarbons such as n-butane over a catalyst containing a phosphate of germanium, tin, lead, arsenic, antimony or bismuth, preferably tin. By combustion of the hydrogen, the heat of reaction necessary for the endothermic dehydrogenation is generated in at least one reaction zone.

EP-A 0 838 534 describes a catalyst for the steam-free dehydrogenation of alkanes, in particular of isobutane, in the presence of oxygen. The catalyst used comprises a platinum group metal, which is applied to a support of tin oxide / zirconium oxide with at least 10% tin. The oxygen content in the feed stream of the dehydrogenation is adjusted so that the amount of heat generated by combustion of hydrogen with oxygen is equal to the amount of heat required for the dehydrogenation.

WO 96/33151 describes a process for the dehydrogenation of a C ₂ -C ₅ alkane in the absence of oxygen over a dehydrogenation catalyst containing Cr, Mo, Ga, Zn or a group VIII metal with simultaneous oxidation of hydrogen formed on a reducible metal oxide such as the oxides of Bi, In, Sb, Zn, Tl, Pb or Te. The dehydration must be interrupted regularly to reoxidize the reduced oxide with an oxygen source. No. 5,430,209 describes a corresponding process in which the dehydrogenation step and the oxidation step proceed in succession and the associated catalysts are spatially separated from one another. Oxides of Bi, Sb and Te and their mixed oxides are used as catalysts for the selective hydrogen oxidation. WO 96/33150 finally describes a process in which, in a first stage, a C ₂ -C ₅ alkane is dehydrogenated on a dehydrogenation catalyst, the exit gas of the dehydrogenation stage is mixed with oxygen and in a second stage via an oxidation catalyst, preferably Bi ₂ θ ₃ , wherein the hydrogen formed is selectively oxidized to water, and in a third stage, the second-stage source gas is again passed through a dehydrogenation catalyst.

US 5,565,775 describes a method for nondestructive determination of bound and free, i. producible, liquid fractions in porous materials (especially on bedrock rocks), which is based on a two-component decomposition of the measured with a Pulsed Field Gradient (PFG) NMR technique self-diffusion behavior of pore liquids trapped in the pore space.

The catalyst system used must have regard to achievable alkane conversion, selectivity for the formation of alkenes, mechanical stability, thermal stability, coking behavior, deactivation behavior, regenerability, stability in the presence of oxygen and insensitivity to catalyst poisons such as CO, sulfur- and chlorine-containing compounds, alkynes etc. and economy meet high requirements.

The object of the invention is to provide dehydrogenation catalysts having improved properties. The object of the invention is in particular to provide dehydrogenation catalysts with improved deactivation behavior.

The object is achieved by a catalyst support made of a support material with a Tortuositätskennzahl τ of 1, 5 to 4, preferably 1, 5 to 3 and particularly preferably 2 to 3. Conveniently, this Tortuositätskennzahl refers in this document, unless otherwise explicitly mentioned to a determination at 25 ° C and 1 bar using H ₂ O as the probe molecule. This is because H ₂ O is able to simulate the diffusion behavior of the relevant reactants in a good approximation.

Particularly preferred catalyst supports according to the present invention are their tortuosity index, determined with the hydrocarbon to be dehydrogenated, for example propane or a butane, such as isobutane at 25 ° C. and 1 bar 1, 5-4, preferably 1.5-3, particularly preferably 2-3 is. Very particular preference is given to catalyst supports whose tortuosity index, determined with the hydrocarbon to be dehydrogenated, but at the temperature used for dehydrogenation and the pressure used for dehydrogenation, is 1.5-4, preferably 1.5-3, particularly preferably 2-3. Even more advantageous are catalyst supports whose tortuosity index, determined with the unsaturated eg propene formed by the dehydrogenation or a butene, eg isobutene hydrocarbon at 25 ° C. and 1 bar, 1, 5 - 4, preferably 1, 5 - 3, particularly preferably 2 - 3, is. Very particular preference is given to catalyst supports whose tortuosity index, determined using the unsaturated hydrocarbon formed by the dehydrogenation, but at the temperature used for dehydrogenation and the pressure used for dehydrogenation, is 1.5-4, preferably 1.5- 3, particularly preferably 2. 3 amounts to.

With regard to the carrier geometry, there are no restrictions according to the invention. Particularly common geometries are solid cylinders, hollow cylinders (rings), spheres, cones, pyramids and cubes. The different geometries can e.g. obtained by tableting or extrusion. The extrusion is particularly suitable for the design of strands, wagon wheels, stars, monoliths or rings. Even split carrier (carrier split) can be used. The longest extent (longest direct connecting line between two points located on the carrier surface) of such carriers is often 0.5 mm to 100 mm, often 1.5 mm to 80 mm, and often 3 mm to 50 mm or up to 20 mm. For carrier beads which are used for catalysts to be used in fluidized-bed reactors, this longitudinal expansion is expediently 0.01 mm to 1 mm, preferably 0.02 to 0.2 mm. For monoliths and foams, e.g. can be used with advantage in low-pressure-loss reactors, this longest extent can be up to 1000 mm.

The object is further achieved by a dehydrogenation catalyst containing one or more active masses on a catalyst support (in particular on the inner surface by appropriate impregnation) from a support material with an aforementioned Tortuositätskennzahl (determined with water, or the hydrocarbon to be dehydrogenated, or the at Dehydrogenation unsaturated hydrocarbon) τ of 1, 5 to 4, preferably 1, 5 - 3, more preferably 2 - 3. The active mass usually contains at least one active metal in elemental form, but it can also be exclusively of oxidic nature ,

The tortuosity index τ of a catalyst support material is determined according to a further aspect of the invention by determining the self-diffusion D (self-diffusion coefficient, hereinafter referred to as "self-diffusion") of a probe gas or a probe liquid in the support material and the self-diffusion D _{0 of} the free gas or the free liquid determined as the quotient τ = D / D ₀ under the corresponding boundary conditions (25 ° C, 1 bar) (see below). A free gas or a free liquid is understood to mean a gas or a liquid whose extent is much greater than the mean free path of the molecules and surface effects can be neglected with respect to their extent.

Preferred support for dehydrogenation catalysts according to the invention contain as support material a metal oxide, e.g. selected from the group consisting of zirconium oxide, aluminum oxide, silicon dioxide, titanium dioxide, magnesium oxide, lanthanum oxide and cerium oxide and mixtures thereof. The mixtures may be physical mixtures or chemical mixed phases such as magnesium or zinc-aluminum oxide mixed oxides. In principle, suitable carrier materials are both (for example the abovementioned) metal oxides themselves and also mixtures of metal oxides or mixed metal oxides. Dehydrogenation catalysts which are particularly suitable according to the invention comprise on the support according to the invention at least one element of subgroup VIII, or at least one element of main group I or II, or at least one element of III. or IV. main group, or at least one element of III. Subgroup, including the lanthanides and actinides, each in metallic and / or chemically bound form.

Very particularly preferred dehydrogenation catalysts comprise on the support according to the invention at least one element of subgroup VIII, at least one element of main group I and / or II, at least one element of IM. and / or IV. main group and at least one element of IM. Subgroup, including the lanthanides and actinides, in metallic or chemically bound form. Preferably, the elements of VIII. Subgroup and of the IV. Main group are present in elemental form and the other elements in oxidic form of the aforementioned elements.

The invention further provides a process for the heterogeneously catalyzed dehydrogenation of one or more dehydrogenatable C ₂ -C ₃₀ hydrocarbons, preferably one or more C ₂ -C ₅ hydrocarbons, more preferably one or more C ₂ -Ce -KOH bons and very particularly preferably by one or more C ₃ - and C ₄ - hydrocarbons in a this-containing reaction gas mixture in which the reaction gas mixture, which contains the, or the dehydrogenatable hydrocarbon is contacted with at least one erfindungsge- MAESSEN dehydrogenation catalyst in contact.

It has been found that catalysts based on the catalyst supports according to the invention having the specified tortuosity have a particularly favorable deactivation behavior, ie are deactivated particularly slowly during the reaction. The tortuosity coefficient (or "labyrinth factor") of a porous material closely approximates the square of the ratio of the length [L) of the shortest connection between two points in the pore space that runs completely through the pore space to the geometric distance of these points [L ₀ ). (Equation 1):

wherein the geometric distance of the points is large compared to characteristic dimensions of the pore space such as pore or grain diameter. It follows that the tortuosity of a porous material is greater than or equal to 1.

For transport processes that run through the pore space, the tortuosity describes the square of the extension of the transport path due to the geometric hindrance at the pore / matrix interface. In addition to the porosity (Φ), the tortuosity thus represents an important parameter that determines transport parameters in porous materials. In transport diffusion processes, for example, it is expected that the diffusion coefficient of a fluid in the porous material (D _teff ) is _reduced by the quotient of porosity and tortuosity compared to the free fluid (D _t ) (Eq

2):

^D ', ff = γ ^D <( ² )

If one observes the self-diffusion of liquids in the pore space over distances that are large compared to the pore size, one notes that the self-diffusion coefficient in the pore space (D) is compared to the value measured in the free liquid (D ₀ ). just reduced by the tortuosity (equation 3):

D = -D ₀ (3)

T

The self-diffusion coefficients of the free liquid D ₀ and the same liquid in a porous material D can be measured directly, for example, by means of PFG NMR (Pulsed Field Gradient Nuclear Magnetic Resonance). Alternatively, tracers (eg radioactive) can be used. The ratio D ₀ ID then gives the tortuosity of the porous material.

The greater the tortuosity of the transport pores in the catalyst particles, the longer does it take for reactant and product molecules to pass between the catalytically active centers. ren exchange at the pore / matrix interface of the catalyst particles and the catalyst particles flowing around the reaction medium by diffusion. If the residence time of the educt and product molecules in the catalyst particles has an influence on the catalytic properties, such as selectivity, activity and deactivation behavior, changes in the tortuosity of the transport pore system of the catalyst particles can lead to changes in the catalytic catalyst Properties lead. The reason for this is the influence of the tortuosity on the mean residence time f _{e / p of} the reactant and product molecules, which can be estimated from the diffusion coefficient under reaction conditions (D _{e / p} ) and the radius R of spherical catalyst particles (equation 4):

R. ..

' ^• " ^{= τ'} ϊ ^ ⁽⁴⁾

For non-spherical (e.g., cylindrical) catalyst particles, R in Equation (4) denotes the corresponding equivalent radius.

Dehydrogenation catalysts in which the active composition has been applied to the inner surface of the support are therefore advantageous according to the invention in that the tortuosity of the finished catalyst essentially corresponds to that of the support used. Preferred catalysts are therefore also those having corresponding tortuosity parameters (determined with water or the hydrocarbon to be dehydrogenated, or the unsaturated hydrocarbon formed during the dehydrogenation) of 1.5 to 4, preferably 1.5 to 3, particularly preferably 2 - 3.

The PFG NMR allows the non-destructive investigation of self-diffusion, ie the thermally induced Brownian molecular motion of free gases and liquids, of macromolecular solutions and melts as well as of adsorbed molecules and liquids in the pore space of porous materials. The prerequisite is that the molecules of the substances to be investigated (gases or liquids) contain in their molecular structure at least one atom with a non-vanishing nuclear spin / and thus with the magnetic nuclear magnetic resonance (NMR) transitions between the Zeeman energy levels of the nuclear spins / in a strong external magnetic field (S ₀ ) can be observed.

Principle, Performance and Application of PFG NMR measurements are described in the following references: (1) EO Stejskal, JE Tanner, J. Chem. Phys. 42, 288-292 (1965). (2) Stallmach, F., Seiffert, G., Kärger, J., Kaess, U., and Majer, G., J. Magn. Reson. 151, 260-268 (2001); (3) Kärger, J., Papadakis, Ch. M., and Stallmach, F. Structure Mobility Relations of Molecular Diffusion in Interface Systems, in Lecture Notes in Physics, vol. 634, publisher: R. Stanarius, A. Pöppel, R. Haber lands and D. Michel, Springer Verlag, 2004; (4) Stallmach, F., and Kärger, J., Adsorption 5, 17-133 (1999); (4) Kärger, J. and MD Ruthven, Diffusion in Zeolites and other Microporous Solids, Wiley-Interscience, New York, 1992, and Callaghan, PT, Principles of Nuclear Magnetic Resonance Microscopy, Clarendon Press, Oxford, 1991.

In PFG-NMR, a so-called spin echo of the nuclear spins is first generated by irradiating short high-frequency magnetic field pulses (RF pulses). The intensity of this spin echo NMR signal is proportional to the number of resonant nuclear spins in the study volume and is determined by the time between the excitation by the first RF pulse to the spin maximum (t _e ) by spin lattice ^) and spin spin. (7 ₂ ) relaxation processes dampened. FIGS. 1 a - c show by way of example three different pulse programs for the generation of such spin echo NMR signals. In the time intervals of the pulse sequences b (stimulated spin echo, STE) and c (13-interval pulse train) marked with Δ ', the nuclear spins are subject to T ₁ relaxation. During all other times and in the pulse sequence a (Hahn's spin echo, SE), they are only subject to the 7 ₂ -Relaxation.

For the measurement of the self-diffusion, a _spatially dependent magnetic field of the form B _ιnh (z) = gz is superimposed on the external magnetic field S ₀ during these pulse sequences, whereby g and z _{correspond to} the pulsed magnetic field gradients (narrow: pulsed field gradient) Represent location coordinate. The necessary magnetic field gradient pulses are thereby generated via current pulses synchronized to the HF pulse sequence, which flow through a suitable magnet coil combination (the gradient coils). Because, during the duration of the field gradient pulses, the resonance condition for the nuclear spins is location dependent and the probe molecules diffuse to another location between successive field gradient pulses due to self-diffusion, the amplitude of the observed spin echo is attenuated. This spin echo attenuation Ψ as a function of the duration (δ), intensity (g) and the interval spacing (Δ) of the magnetic field gradients is the observed variable in the PFG NMR. From this follows the self-diffusion coefficient D (A) of the molecules according to equation (5)

Ψ (gδ, Δ) _{≡ 1} 0! 0 _y = exp [-M) (Δ)]. (5)

The size b depends on the pulse train used. It is calculated from the measurement parameters of the respective PFG NMR pulse train. For the pulse sequence shown by way of example in FIG. 1, the size b results in:

In this case, γ denotes the gyromagnetic ratio of the observed nuclear spins. The term dependent on the pulse sequence in the parenthesis in Eq. (6) is the effective diffusion time. For short field gradient pulses it is dominated by the time Δ, that is to say the spacing of the field gradient pulses of the same polarity (see FIG. 1), and is a variable known and variable in the PFG NMR experiment.

Experimentally, one usually measures the spin echo damping curves for a fixed interval Δ and a fixed duration δ of the field gradient pulses and varies their intensity g. The self-diffusion coefficient D (A) for the associated diffusion time Δ results according to Eq. (5) from the slope of a plot of InΨ versus -b. Using Einstein's equation, the mean square displacement during the diffusion time can be calculated from D (A) (Equation 7):

(r ² (Δ)) = 6 £> (Δ) Δ (7)

The present invention also provides a method for determining the tufting of a catalyst support material by determining the self-diffusion D of a gas or a liquid in the support material and the self-diffusion D _{0 of} the free gas or the free liquid, in which expediently

(i) a gas or a liquid containing molecules having at least one atom with non-vanishing nuclear spin I ("probe molecules") is introduced into the pore space of a sample of the carrier material,

(ii) an external magnetic field B _{0 is} generated at the location of the sample of the carrier material,

(iii) a spin choke of the nuclear spins I in the sample is produced by irradiation of short high-frequency magnetic field pulses,

(iv) δ for several short time intervals the external magnetic field B ₀ is a location-dependent magnetic field B is superimposed as Feldgradientenimpuls, whereby the amplitude of the observed spin echo is attenuated and thus a Spine- chodämpfung Ψ as a function of pulse duration δ, the intensity g and the time interval Δ of the field gradient pulses is measured, (v) from the spin echo damping Ψ the self-diffusion coefficient D of the gas or liquid molecules in the sample is determined,

(vi) carrying out the steps (i) to (v) with a sample of the free gas or of the free liquid, whereby a self-diffusion coefficient D _{0 of} the molecules of the free gas or of the free liquid is determined,

(vii) the tortuosity factor τ is obtained as the quotient of the self-diffusion coefficient D _{0 of} the free gas or of the free liquid and the self-diffusion coefficient D of the gas or of the liquid in the carrier material τ = D ₀ / D.

A preferred probe liquid, which in step (i) is introduced into the pore space of the sample of the carrier material, for example by soaking the sample, is, as already mentioned, water. Alternatively, liquids other than water can also be used as "probe molecules" for tortuosity measurement with PFG NMR: they only need to have atoms with a nuclear spin detectable by NMR (eg, ¹ H, ¹⁹ F, ¹³ C) and wet the porous support material In addition, the vapor pressure of the fluid used should be high enough so that the catalysts do not dry out during the NMR measurement, which can take several hours Suitable further liquids are, for example, cyclooctanes or other linear or cyclic alkanes having 5 or more carbon atoms, but the tortuosity can also be determined using gaseous probe molecules contained in the carrier material (eg propane, butane) has relevant pores, the result achieved by the choice of the probe molecule is essentially u nabhängig.

The support according to the invention generally consists of a (preferably heat-resistant) oxide or mixed oxide (eg steatite). It preferably contains a metal oxide which is selected from the group consisting of zirconium dioxide, zinc oxide, aluminum oxide, silicon dioxide, titanium dioxide, magnesium oxide, lanthanum oxide, cerium oxide and mixtures thereof. The mixtures may be physical mixtures or chemical mixed phases such as magnesium or zinc-aluminum oxide mixed oxides. The tortuosity of said metal oxides can vary widely. Among them, a carrier having suitable tortuosity is selected. However, the tortuosity can also be adjusted in a targeted manner by using (in particular finely divided) nonoxidic or even oxidic carrier starting materials (usually metal-containing compounds which decompose upon thermal treatment and convert into metal oxides, at least on thermal decomposition in air ) in the presence of Po formers (eg by tabletting or extrusion) and then thermally treated.

In a preferred embodiment, the dehydrogenation catalyst according to the invention contains at least one element of subgroup VIII, at least one element of main group I and / or II, at least one element of IM. and / or IV. main group and at least one element of IM. Subgroup including the lanthanides and actinides.

As an element of the VIII. Subgroup contains the active material of the dehydrogenation catalysts preferably platinum and / or palladium, more preferably platinum.

As elements of the I. and / or M. main group, the active composition of the dehydrogenation catalysts according to the invention preferably contains potassium and / or cesium.

As elements of the Ml. Subgroup, including the lanthanides and actinides, the active composition of the dehydrogenation catalysts according to the invention preferably contains lanthanum and / or cerium.

As elements of the Ml. and / or IV. Main group contains the active material of the dehydrogenation catalysts according to the invention preferably one or more elements from the group consisting of boron, gallium, silicon, germanium, tin and lead, particularly preferably tin. The active material of a dehydrogenation catalyst according to the invention very particularly preferably contains at least one member of the abovementioned element groups.

The catalytic hydrocarbon dehydrogenation can in principle be carried out in all reactor types and modes of operation known from the prior art. Hydrogenation A comparatively comprehensive description of the invention suitable De- also contains "Catalytica® ^® Studies Division, Oxidative Dehydrogenation and Alternative Dehydrogenation Processes" (Study Number 4192 OD, 1993, 430 Ferguson Drive, Mountain View, California, 94043-5272, USA).

A suitable reactor form is the fixed bed tube or tube bundle reactor. In these, the catalyst is (dehydrogenation catalyst according to the invention and, when working with oxygen as a co-feed, optionally special oxidation catalyst) as a fixed bed in a reaction tube or in a bundle of reaction tubes. The reaction tubes are usually indirectly heated by burning a gas, for example a hydrocarbon such as methane, in the space surrounding the reaction tubes. It is beneficial, this indirect form of heating only on the apply the first approximately 20 to 30% of the length of the fixed bed and to heat the remaining bed length to the required reaction temperature by the radiant heat released during indirect heating. Typical reaction tube internal diameters are about 10 to 15 cm. A typical dehydrogenation tube bundle reactor comprises about 300 to 1000 reaction tubes. The temperature inside the reaction tube usually moves in the range of 300 to 1200 ° C, preferably in the range of 500 to 1000 ° C. The working pressure is usually between 0.5 and 8 bar, often between 1 and 2 bar using a low water vapor dilution (according to the Linde process for propane dehydrogenation), but also between 3 and 8 bar when using a high water vapor dilution (corresponding to the so-called "steam active reforming process" (STAR process) for the dehydrogenation of propane or butane by Phillips Petroleum Co., see US 4,902,849, US 4,996,387 and US 5,389,342.) Typical Catalyst Exposure (GHSV) is 500 to 2000 h ^-1 , based on the hydrocarbon used. The catalyst geometry can be, for example, spherical or cylindrical (hollow or full).

The non-oxidative catalytic hydrocarbon dehydrogenation may also be carried out as described in Chem. Eng. Be. 1992 b, 47 (9-1 1) 2313, heterogeneously catalyzed in a fluidized bed. Conveniently, two fluidized beds are operated side by side, one of which is usually in the state of regeneration. The working pressure is typically 1 to 2 bar, the dehydration temperature usually 550 to 600 ° C. The heat required for the dehydrogenation is introduced into the reaction system in that the dehydrogenation catalyst is preheated to the reaction temperature. By adding an oxygen-containing co-feed can be dispensed with the preheater, and the heat required directly in the reactor system by combustion of hydrogen and / or hydrocarbons in the presence of oxygen are generated. Optionally, a hydrogen-containing co-feed may additionally be admixed.

The non-oxidative catalytic hydrocarbon dehydrogenation can be carried out with or without oxygen-containing gas as a co-feed in a tray reactor. This contains one or more consecutive catalyst beds. The number of catalyst beds may be 1 to 20, advantageously 1 to 6, preferably 1 to 4 and in particular 1 to 3. The catalyst beds are preferably flowed through radially or axially from the reaction gas. In general, such a tray reactor is operated with a fixed catalyst bed. In the simplest case, the fixed catalyst beds are arranged in a shaft furnace reactor axially or in the annular gaps of concentrically arranged cylindrical gratings. A shaft furnace reactor corresponds to a horde. Carrying out the dehydrogenation in a single shaft furnace reactor corresponds to a preferred embodiment, which can be carried out with oxygen-containing co-feed. In a further preferred embodiment, the dehydrogenation is carried out in a tray reactor with 3 catalyst beds. In a procedure without oxygen-containing gas as a co-feed, the reaction gas mixture in the tray reactor is subjected to intermediate heating on its way from one catalyst bed to the next catalyst bed, for example by passing over heated with hot gases heat exchanger surfaces or by passing through heated with hot fuel gases pipes.

In a preferred embodiment of the process according to the invention, the non-oxidative catalytic hydrocarbon dehydrogenation is carried out autothermally. For this purpose, oxygen is added to the reaction gas mixture of the hydrocarbon dehydrogenation in at least one reaction zone and at least partially combusted the hydrogen and / or hydrocarbon contained in the reaction gas mixture, whereby at least part of the required Dehydrierwärme in the at least one reaction zone is generated directly in the reaction gas mixture.

In general, the amount of the oxygen-containing gas added to the reaction gas mixture is selected such that the amount of heat required for the dehydrogenation of the hydrocarbon is produced by the combustion of hydrogen present in the reaction gas mixture and optionally by hydrocarbons present in the reaction gas mixture and / or by coke is produced. In general, the total amount of oxygen fed, based on the total amount of butane, is 0.001 to 0.5 mol / mol, preferably 0.005 to 0.2 mol / mol, particularly preferably 0.05 to 0.2 mol / mol. Oxygen can be used either as pure oxygen or as an oxygen-containing gas mixed with inert gases, for example in the form of air. The inert gases and the resulting combustion gases generally additionally dilute and thus promote the heterogeneously catalyzed dehydrogenation.

The hydrogen burned to generate heat is the hydrogen formed during the catalytic hydrocarbon dehydrogenation and, if appropriate, the hydrogen gas additionally added to the reaction gas mixture as hydrogen. Preferably, sufficient hydrogen should be present so that the molar ratio H ₂ / O ₂ in the reaction gas mixture immediately after the introduction of oxygen is 1 to 10, preferably 2 to 5 mol / mol. This applies to multi-stage reactors for each intermediate feed of oxygen-containing and optionally hydrogen-containing gas. The hydrogen combustion takes place catalytically. The dehydrogenation catalyst used generally also catalyzes the combustion of the hydrocarbons and of hydrogen with oxygen, so that in principle no special oxidation catalyst different from this one is required. In one embodiment, work is carried out in the presence of one or more oxidation catalysts which selectively catalyze the combustion of hydrogen with oxygen in the presence of hydrocarbons. The combustion of these hydrocarbons with oxygen to CO, CO ₂ and water is therefore only to a minor extent. Preferably, the dehydrogenation catalyst and the oxidation catalyst are present in different reaction zones.

In multi-stage reaction, the oxidation catalyst may be present in only one, in several or in all reaction zones.

Preferably, the catalyst which selectively catalyzes the oxidation of hydrogen is disposed at the sites where higher oxygen partial pressures prevail than at other locations of the reactor, particularly near the oxygen-containing gas feed point. The feeding of oxygen-containing gas and / or hydrogen-containing gas can take place at one or more points of the reactor.

In one embodiment of the method according to the invention, an intermediate feed of oxygen-containing gas and of hydrogen-containing gas takes place before each tray of a tray reactor. In a further embodiment of the method according to the invention, the feed of oxygen-containing gas and of hydrogen-containing gas takes place before each horde except the first horde. In one embodiment, behind each feed point is a layer of a specific oxidation catalyst, followed by a layer of the dehydrogenation catalyst. In another embodiment, no special oxidation catalyst is present. The dehydrogenation temperature is generally from 400 to 1100 ° C., the pressure in the last catalyst bed of the tray reactor generally from 0.2 to 5 bar, preferably from 1 to 3 bar. The load (GHSV) is generally 500 to 2000 h ^"1 , in high load mode also up to 100 000 h ^{" 1} , preferably 4000 to 16 000 h ^"1 .

A preferred catalyst which selectively catalyzes the combustion of hydrogen contains oxides and / or phosphates selected from the group consisting of the oxides and / or phosphates of germanium, tin, lead, arsenic, antimony or bismuth. Another preferred catalyst which catalyzes the combustion of hydrogen contains a noble metal of VIII. And / or I. Nebengruppe. The hydrocarbon dehydrogenation is preferably carried out in the presence of steam. The added water vapor serves as a heat carrier and supports the gasification of organic deposits on the catalysts, whereby the coking of the catalysts counteracted and the service life of the catalysts is increased. The organic deposits are converted into carbon monoxide, carbon dioxide and possibly water.

Preferred C ₂ -C 30 -hydrocarbons which are dehydrogenated according to the invention are propane and butane.

The dehydrogenation catalyst according to the invention can be regenerated in a manner known per se. Thus, steam can be added to the reaction gas mixture or, from time to time, an oxygen-containing gas can be passed over the catalyst bed at elevated temperature and the deposited carbon burned off. Dilution with water vapor shifts the equilibrium to the products of dehydration. Optionally, the catalyst is reduced after regeneration with a hydrogen-containing gas.

The process according to the invention is particularly advantageous when the reaction gas mixture passed over the dehydrogenation catalyst already contains dehydrogenated hydrocarbon, as described e.g. in the processes of the publications DE-A 102005009885, DE-A 102005022798, WO 01/96270, WO 01/96271, WO 03/01 1804, WO 03/76370, DE-A 10245585, DE-A 102461 19, DE-A 10316039, DE-A 102004032129, DE-A 10200501011 1, DE-A 102005013039 and DE-A 102005009891 is described in detail. In all of the dehydrogenation processes mentioned in these documents, catalysts according to the invention are particularly suitable.

The invention is explained in more detail by the following examples. The following supports are especially good catalyst supports if the pore volume is in the range of 0.12-0.4 ml / g (measured by Hg porosimetry). The pore distribution can be unimodal, bimodal or polymodal.

The inventive method is particularly advantageous in that the determination of tortuosity in a much simpler manner than in the past allows the selection of suitable carriers or dehydrogenation catalysts. In the past, this always required elaborate dehydrogenation experiments. Examples

Examples 1 to 6

The following catalyst supports were used in the experiments described below:

Preparation of a ZrO ₂ spray powder:

72.6 kg of concentrated aqueous nitric acid (69% by weight of HNO 3) were initially introduced into a 500 l kettle and 58.7 kg of Zr (IV) carbonate (Co., Ltd.) were added uniformly with stirring (20 rpm) over the course of 2 hours MEL, Luxfer Group Company, about 43% by weight ZrO ₂ ). A zirconyl nitrate solution containing about 19% by weight of ZrO ₂ and a density of 1.59 kg / l was obtained. In a stirred tank (1000 l) 135.8 kg of ammonia water (12.5 wt .-% NH ₃ ) were submitted. For this purpose, the zirconyl nitrate solution was pumped in uniformly with stirring within 2 h. The pH of the precipitation reached was 5.2 at 25 ° C. After stirring for 6 h, the suspension was pumped onto a filter press and washed with a total of 15 m ^{3 of} demineralized water over a period of 14 h until the conductivity of the washing water at 25 ° C. was below 20 μS / cm. There were obtained 85.6 kg of wet filter paste. The filter paste was spread on sheets (layer height 10 cm) and dried in a box furnace from Naber at 450 ° C for 8 h under air. (Alternatively, the heat treatment may be carried out under H ₂ O vapor (1 bar), and the resulting ZrO ₂ powders are to be used in Examples 1-1 1 and Comparative Example, and a rotary kiln may be used instead of a Neber furnace The resulting ZrO ₂ powder is then used analogously in Examples 1-1 1 and Comparative Example). The material had an ignition loss of 2.31% by weight at 900 ° C. in air. The XRD measurement showed a proportion of 73% monoclinic and 27% tetragonal ZrO ₂ . Unless otherwise stated, the above steps were carried out at room temperature.

The ZrO ₂ powder (particle diameter in the range of 0.3-100 microns, wherein 50 wt .-% of the particles have a particle diameter <10 microns) was used to prepare the carrier 1 to 6 according to Examples 1 to 6. The tortuosity data are mean values from 2 measurements.

The pore diameter distribution of the ZrO ₂ powder determined by means of mercury porosimetry is reproduced in the table below. Table 1 :

Instead of the polyethylene oxide used in each case with molecular weights in the range of 2.5-3.0 × 10 ⁶ g / mol, it is also possible to use other polyethylene oxides having molecular weights in the range of 10 ⁵ -8 × 10 ⁶ g / mol. In the inventive sense, however, the use of the specified polyethylene oxides is particularly favorable.

example 1

3000 g of ZrO ₂ powder were mixed in a Koller with 90 g of polyethylene oxide (Alkox ^® E 100, KOWA American Corporation) and treated with 90 g of concentrated aqueous nitric acid (69 wt .-% HNO ₃ ). For this purpose, 317 g Silres MSE 100 ^® (Wacker, 70 wt .-% strength SiO ₂ solution) and 500 ml of water. After 5 minutes of mulling, another 150 ml of water was added. After a further 20 minutes of mulling at room temperature, the kneaded material was pressed in an extruder at a pressure of 280 bar into strands with a diameter of 1, 5 mm. After 16 h of drying at 120 ° C in air, the strands were annealed for 4 h at 560 ° C in air. The support thus obtained had a tortuosity of 2.15, measured with H ₂ O at 25 ° C and 1 bar pressure.

Example 2

3000 g of ZrO ₂ powder and 120 g of polyethylene oxide (Alkox E 100, KOWA American Corporation) were mixed in a Koller and treated with 90 g of concentrated aqueous nitric acid (69 wt .-% HNO ₃ ). For this purpose, 350 g Silres MSE 100 (Wacker, 70 wt .-% SiO ₂ solution) and 500 ml of water were added. After 5 minutes of mulling, another 250 ml of water was added. After a further 30 minutes of mulling at room temperature, the kneading material was pressed in an extruder at a pressure of 280 bar to strands with a diameter of 1, 5 mm. After 16 h of drying at 120 ° C in air, the strands were at 4 h at Tempered 600 ° C in air. The support thus obtained had a tortuosity of 2.55, measured with H ₂ O at 25 ° C and 1 bar pressure. Example 3

In a Koller 3000 g of ZrO ₂ powder were mixed with 150 g of polyethylene oxide (Alkox E 100, KOWA American Corporation) and mixed with 120 g of concentrated aqueous nitric acid (69 wt .-% HNO ₃ ). To this was added 500 g of Silres MSE 100 (Wacker, 70% strength by weight SiO ₂ solution) and 500 ml of water. After 5 minutes of mulling, another 250 ml of water was added. After a further 30 minutes of mulling at room temperature, the kneading material was pressed in an extruder at a pressure of 280 bar to strands with a diameter of 1, 5 mm. After 16 h of drying at 120 ° C in air, the strands were annealed for 4 h at 600 ° C in air. The support thus obtained had a tortuosity of 2.95, measured with H ₂ O at 25 ° C and 1 bar pressure.

Example 4

In a muller 3000 g of ZrO ₂ powder with 100 g cellulose ether (Optamix ^® AT 100, Zschimmer & Schwarz GmbH & Co KG) and mixed with 120 g of concentrated aqueous nitric acid (69 wt .-% HNO ₃₎ was added. To this was added 300 g of silica MSE 100 (Wacker, 70% strength by weight SiO ₂ solution) and 500 ml of water. After rinsing for 5 minutes, an additional 250 ml of water were added. After a further 30 minutes of mulling at room temperature, the kneading material was pressed in an extruder at a pressure of 280 bar to strands with a diameter of 1, 5 mm. After 16 h of drying at 120 ° C in air, the strands were annealed for 4 h at 600 ° C in air. The support thus obtained had a tortuosity of 5.45, measured with H ₂ O at 25 ° C and 1 bar pressure.

Example 5

In a Koller 3000 g of ZrO ₂ powder were mixed with 150 g of polyethylene oxide (Alkox E 100, KOWA American Corporation) and mixed with 120 g of concentrated aqueous nitric acid (69 wt .-% HNO ₃ ). To this was added 500 g Siles MSE 100 (Wacker, 70% strength by weight SiO ₂ solution) and 500 ml water. After 5 minutes of mulling, another 250 ml of water was added. After a further 30 minutes of mulling at room temperature, the kneaded material was pressed in an extruder at a pressure of 280 bar to strands with a diameter of 3 mm. After 16 h of drying at 120 ° C in air, the strands were annealed for 4 h at 600 ° C in air. The catalyst support was comminuted to chippings, whereby a sieve fraction of 1, 6 - 2 mm was obtained. The support thus obtained had a tortuosity of 2.8, measured with H ₂ O at 25 ° C and 1 bar pressure. Example 6

3000 g of ZrO ₂ powder were mixed in a Koller with 90 g of polyethylene oxide (Alkox E 100, company KOWA American Corporation) and mixed with 90 g of concentrated aqueous nitric acid (69 wt .-% HNO ₃ ). To this was added 317 g of Silres MSE 100 (Wacker, 70% strength by weight SiO ₂ solution) and 500 ml of water. After 5 minutes of rinsing, an additional 150 ml of water were added. After a further 20 minutes of mulling at room temperature, the kneading material was pressed in an extruder at a pressure of 280 bar into strands with a diameter of 3 mm. After 16 h of drying at 120 ° C, the strands were annealed for 4 h at 560 ° C in air. The catalyst support was comminuted to chippings, whereby a sieve fraction of 1, 6 - 2 mm was obtained. The support thus obtained had a tortuosity of 2.3, measured with H ₂ O at 25 ° C and 1 bar pressure.

Carrying out the PFG-NMR self-diffusion measurements on the water-saturated catalyst supports 1 - 6:

The NMR measurements were carried out at 25 ° C and 1 bar at 125 MHz ¹ H resonance frequency with the NMR spectrometer FEGRIS NT at the Faculty of Physics and Geosciences shadow of the University of Leipzig. The stimulated spin echo with pulsed field gradients according to FIG. 1b was used as a pulse program for the PFG NMR self-diffusion investigations. For each sample, the spin echo attenuation curves were measured with up to six different diffusion times (Δ / ms = 20, 40, 80, 160, 240, 320) by stepwise increasing the intensity of the field gradients {g _ma χ = 4 T / m). From the spin echo damping curves, the time dependence of the self-diffusion coefficient of the pore water was determined by means of equations (2) and (3).

Calculation of tortuosity:

From equation (7), the self-diffusion coefficient D (A) thus determined became

Time dependence of the mean square displacement (r ² (Δ) y calculated. In Figure 2, these data are plotted double-logarithmically along with the corresponding results for free water for the catalyst carrier 1 to 7. In addition, Figure 2 shows in each case the best fit straight line from the linear fit of (r ² (A)) as a function of the diffusion time Δ. Its increase corresponds to Equation (7)

Value 6D, where D corresponds to the self-diffusion coefficient averaged over the diffusion time interval. According to equation (6), the tortuosity then results from the ratio of the thus determined mean self-diffusion coefficient of the free one Water to the corresponding value of the mean self-diffusion coefficient in

Catalyst support.

The tortuosity values thus determined are summarized in Table 2 for the catalyst supports 1-6, with two independently prepared samples from the same batch being measured per catalyst support.

Table 2:

Catalyst support 1. Measurement 2. Measurement Example τ T

1 2.2 ± 0.1 2.1 ± 0.1

2 2.6 ± 0.2 2.5 ± 0.2

3 2.8 ± 0.1 3.1 ± 0.1

4 4.9 ± 0.1 6.0 ± 0.1

5 2.6 ± 0.2 3.0 ± 0.2

6 2.4 ± 0.2 2.2 ± 0.2

Examples 7 to 11 and Comparative Example C1

Preparation of Catalysts 1 to 6 Based on Catalyst Carriers 1 to 6: Catalyst supports 5 and 6 were comminuted to give a sieve fraction of 1.6 to 2 mm. The catalyst supports 1 to 4 were used as 1.5 mm strands (natural fracture). The support materials were coated with the active components Pt / Sn / K / Cs and La according to the method described below:

0.1814 g H ₂ PtCl ₆ ^* 6H ₂ O and 0.2758 g SnCl ₂ ^* 2 H ₂ O were dissolved in 138 ml of ethanol and at 25 ° C in a rotary evaporator to 23 g of the support material. The supernatant ethanol was stripped off on a rotary evaporator while rotating in a water jet pump vacuum (20 mbar) at a water bath temperature of 40.degree. The mixture was then dried under standing air initially at 100 ° C. for 15 h and then calcined at 560 ° C. (under stagnant air) for 3 h. Thereafter, the dried solid with a solution of 0.1773 g CsNOß was 0.3127 g of KNO3 and 2.2616 g La (NO ₃₎ ₃ ^* 6 H ₂ O in 55 ml H ₂ O at 25 ° C is poured over. The supernatant water was removed from the rotavapor while rotating in a water pump vacuum (20 mbar) at a water bath temperature of 85.degree. Subsequently, the mixture was first dried under standing air at 100 ° C. for 15 h and then calcined at 560 ° C. under stagnant air for 3 h. The catalysts 1 to 6 were thus obtained from catalyst supports 1 to 6. The catalysts thus obtained were installed in a test reactor and activated.

Katalvsatoraktivierung:

With 20 ml of the obtained catalyst precursor, a vertically standing tube reactor was charged.

Reactor length: 520 mm; Wall thickness: 2 mm;

Inner diameter: 20 mm;

Reactor material: internally alonized, i. aluminum oxide coated steel pipe;

Heating: electrically on a longitudinal center length of 450 mm;

Length of catalyst bed: 60 mm; Position of the catalyst bed: longitudinally centered;

Filling the reactor residual volume up and down with steatite balls of a

Diameter of 4 - 5 mm as inert material, sitting down on a contact chair.

Subsequently, the reaction tube was charged at an outside wall temperature along the heating zone of 500 ° C with 9.3 Nl / h of hydrogen for 30 min. Subsequently, the hydrogen flow was maintained at a constant wall temperature for 30 minutes by a stream of 23.6 Nl / h from 80 vol .-% nitrogen and 20 vol .-% air and then for another 30 minutes by an equal stream of pure air replaced. While maintaining the wall temperature was then flushed with an equal current of N ₂ 15 min long and finally reduced again for 30 minutes with 9.3 Nl / h of hydrogen. This completed the activation of the catalyst precursor.

Catalysis test:

Following activation, the catalysts were tested by being charged in the same reactor with a mixture of 20 Nl / hr crude propane, 18 g / hr water vapor, and 1 Nl / hr nitrogen. Raw propane was metered in by means of a mass flow controller, while water was first metered into an evaporator in liquid form by means of an HPLC pump, evaporated therein, and then mixed with the crude propane and nitrogen. The gas mixture was passed over the catalyst. The wall temperature was 622 ° C.

By means of a pressure control located at the reactor outlet, the outlet pressure of the reactor was set to 1.5 bar absolute. The product gas, which had been expanded to atmospheric pressure behind the pressure control, was cooled, with the water vapor condensed out. The uncondensed residual gas was analyzed by GC (HP 6890 with Chem-Station, detectors: FID, WLD, separation columns: AI ₂ O ₃ / KCI (Chrompack), Carboxene 1010 (Supelco)). In a similar manner, the reaction gas [feed gas stream] had been analyzed.

Table 3 summarizes the average tortuosity for catalysts 1-6, the BET surface area determined by means of N ₂ adsorption, the activity (based on the propane conversion) and the deactivation of the catalysts.

Table 3

The deactivation of the catalyst is correlated with the average tortuosity (τ). The inner surface of the catalyst (BET surface area) correlates neither with tortuosity nor with deactivation. The reported conversion represents the propane conversion at the beginning of the dehydrogenation test, the decrease in% per hour is a measure of the deactivation of the catalyst. As can be seen from the examples, the catalysts according to the invention have a much lower deactivation compared to the comparative catalyst with essentially comparable BET surface area.

Claims

claims

1. A method for determining the tortuosity of a porous catalyst support material by determining the self-diffusion D of a gas or a liquid in the support material and the self-diffusion D _{0 of} the free gas or the free liquid and calculation of the quotient D / D _o .

2. The method according to claim 1, characterized in that

(i) a gas or a liquid containing molecules having at least one atom with non-disappearing nuclear spin I is introduced into the pore space of a sample of the carrier material,

(iii) generating a spin echo of the nuclear spins I in the sample by irradiation of short high-frequency magnetic field pulses,

(iv) superimposed on the external magnetic field B ₀ a field-dependent magnetic field B as a field gradient pulse during several short time intervals δ, whereby the amplitude of the observed spin echo is attenuated and thus a spin echo damping Ψ as a function of the pulse duration δ, the intensity g and the time interval Δ Field gradient pulses is measured,

(V) from the spin echo damping Ψ the self-diffusion coefficient D of Gasbzw. Liquid particles in the sample is determined

(vi) the step (i) to (v) with a sample of the free gas or the free

Liquid are carried out, whereby a self-diffusion coefficient D _{0 of} the free gas or the free liquid is determined,

(vii) the tortuosity factor τ is obtained as a quotient of the self-diffusion coefficient D _{0 of} the molecules of the free gas or of the free liquid and the self-diffusion coefficient D of the molecules of the gas or of the liquid in the carrier material τ = D ₀ / D.

3. The method according to claim 2, characterized in that the gas or liquid, which is introduced in step (i) in the pore space of a sample of the carrier material, water.

4. catalyst support of a porous support material with a Tortuosi- tätskennzahl τ of 1, 5 to 4.

5. Catalyst support according to claim 4 from a porous support material with a Tortuositätskennzahl τ of 1, 5 to 3.

6. Catalyst support according to claim 5 from a porous support material with a Tortuositätskennzahl τ of 2 to 3.

7. A catalyst support according to any one of claims 4-6, characterized in that the support material comprises a metal oxide selected from the group consisting of zirconia, alumina, silica, titania, magnesia, lanthana and ceria.

8. dehydrogenation catalyst having improved deactivation behavior, comprising one or more active metals in elemental form and / or oxidic form on a catalyst support according to one of claims 4 to 7.

9. dehydrogenation catalyst according to claim 8, characterized in that it comprises at least one element of the VIII. Subgroup, at least one element of the I. or II. Main group, at least one element of the IM. or IV. Main group and at least one element of IM. Subgroup, including the lanthanides and actinides, in elemental form and / or oxidic form on the catalyst support.

10. dehydrogenation catalyst according to claim 8 or 9, characterized in that it contains platinum and / or palladium in elemental form.

1 1. Dehydrogenation catalyst according to one of claims 8 to 10, characterized in that it contains cesium and / or potassium in oxidic form.

12. dehydrogenation catalyst according to any one of claims 8 to 11, characterized in that it contains lanthanum and / or cerium in oxidic form.

13. dehydrogenation catalyst according to any one of claims 8 to 12, characterized in that it contains tin.

14. dehydrogenation catalyst consisting of a porous support body and a self-applied thereto active mass, characterized in that it has a Tortuositätskennzahl τ of 1, 5 to 4.

15. A process for the heterogeneously catalyzed dehydrogenation of one or more dehydrogenatable C ₂ -C ₃₀ -hydrocarbons in a this-containing reaction gas mixture, characterized in that the reaction gas mixture, which contains the, or the dehydrogenatable hydrocarbons with a dehydrogenation catalyst according to any one of claims 8 until 14 is brought into contact.

16. The method according to claim 15, characterized in that the dehydrogenation is carried out autothermally by at least part of the dehydrogenation heat required in at least one reaction zone by combustion of hydrogen, the educt and / or product hydrocarbons and / or of Carbon is generated in the presence of an oxygen-containing gas directly in the reaction gas mixture.

17. The method according to claim 15 or 16, characterized in that the de-hydrogenatable hydrocarbon is propane and / or butane.

18. The method according to claim 15 to 17, characterized in that the reaction onsgasausgangsgemisch already contains dehydrogenated hydrocarbon.

19. A method for determining the tortuosity of a catalyst comprising a porous support material and an active mass applied thereto by determining the self-diffusion D of a gas or a liquid in the catalyst and the self-diffusion D _{0 of} the free gas or the free liquid and calculation of the Quotients D / D _o .

20. The method according to claim 19, characterized in that

(i) introducing into the pore space of a sample of the catalyst a gas or a liquid containing molecules having at least one atom with nonspinous nuclear spin I, (ii) an external magnetic field B _{0 is} generated at the location of the sample of the catalyst,

(v) from the spin echo damping Ψ the self-diffusion coefficient D of the gas or liquid particles in the sample is determined,

(vi) performing steps (i) to (v) with a sample of the free gas or the free liquid, respectively, whereby a self-diffusion coefficient D _{0 of} the free gas or the free liquid is determined,

(vii) the tortuosity factor τ is obtained as the quotient of the self-diffusion coefficient D _{0 of} the molecules of the free gas or the free liquid and the self-diffusion coefficient D of the molecules of the gas or liquid in the carrier material τ = D ₀ / D.

21. The method according to claim 20, characterized in that the gas or liquid, which is introduced in step (i) in the pore space of a sample of the catalyst, water.

22. Catalyst comprising a porous support material and an active composition applied thereto with a Tortuositätskennzahl τ of 1, 5 to 4.

23. Catalyst according to claim 22, comprising a porous carrier material and an active composition applied thereto with a Tortuositätskennzahl τ of 1, 5 to 3.

24. Catalyst according to claim 23, comprising a support material and an active mass applied thereto with a Tortuositätskennzahl τ of 2 to 3.

25. A catalyst according to any one of claims 22-24, characterized in that the carrier material comprises a metal oxide selected from the group consisting of zirconia, alumina, silica, titania, magnesia, lanthana and ceria.